1. Field of Invention
This invention relates to a template, specifically, but not by way of limitation to such templates for guiding a marking implement in marking circular lines upon a workpiece surface and, interchangeably, provides for guiding a cutting tool, as a router, in following the marked lines being engaged with the workpiece surface.
2. Description of Prior Art
There are many methods used in marking circular lines upon a workpiece surface and then using a cutting tool, such as a router, complete with a guiding apparatus to follow the scribed circular pattern in cutting engagement with the workpiece. A circle scribing compass or actual sized circular cutout is used to scribe the circular pattern of the selected radius upon the workpiece. Once marked, a separate device, attached to the cutting tool, is employed by setting the pivot on the circle's centerpoint. The radius is set accordingly using the adjustment method provided in matching the path of the cutting bit with the circular pattern as marked. A variety of these guiding devices are disclosed within the prior art which utilize various methods in supporting and guiding the router in following marked or unmarked circular patterns on a workpiece surface. Each have advanced the art but have retained construction, adjustment, and operational disadvantages that are now overcome by the simple and versatile instant invention.
A common device is constructed of a convenient length of wood attached to the base of the router, allowing the cutting bit to extend below and into the workpiece. A nail is driven through the wood at a selected distance, the radius, from the cutting bit and is imbedded into the workpiece surface. Thus anchored, the attached router is rotated 360 degrees around the nail pivot cutting the circular groove.
A more adjustable version of this type was disclosed by Lange in U.S. Pat. No. 3,635,268, issued Jan. 18, 1972, wherein an adjustable sliding guide track was attached to the router base. Robinson in U.S. Pat. No. 4,143,691 issued Mar. 13, 1979 incorporated the apparatus in a permanent router base with mating guide pairs operating in a continuous radial slot.
These and all other variations in the art that provide for the circular guiding apparatus to be securely attached to the router base with screws, clamps or other fasteners, have the following disadvantages:
a) The attached electric power supply cord develops a new twist with each 360 degree rotation. The cord twist must be reversed by rotation of the tool in an opposite direction. Removing the cord plug from the electric receptacle, untwisting the cord, and reconnecting the plug may be done. This stress, can lead to cord breakage, loss of power, and electric shock hazard to the workman.
b) The workman must interrupt a continuous 360 degree cutting rotation about the pivot to exchange handholds on the right and left tool handles if he remains at a single workstation. The practice of releasing a high speed cutting tool can lead to accidents and injury to the workman.
c) The workman must walk completely around the workpiece in maintaining his original handhold on the tool's right and left handles. This is often impossible in small workshops where the workbench is frequently against the shop wall preventing 360 degree walk around movement by the workman.
d) The circular guiding apparatus attached to the base of the router must be elevated above the workpiece surface and held while being rotated about the pivot in order to preview the planned cut to be made when the apparatus is lowered in the cutting engagement with the workpiece surface.
e) Accurate measurements must be made in setting the pivot and the radius required to the cutting bit on the router to insure that the circular cut is constructed on the planned location on the surface. Workmen with impaired vision have difficulty in performing this task.
f) Pivot holes provided in prior art circular guiding apparatus are subject to enlargement by wear, making accurate circular groove or disc cutout repetition difficult as the apparatus is rotated around a loose fitting pivot. As this occurs, the device must either be repaired or retired from use.
g) Sliding arms, bars, and the like attached to the router's base, although providing infinite radii settings, are subject to wear and slippage in adjustment that can lead to miscuts and damage to the workpiece surface.
Another router guiding device for cutting circular grooves is disclosed in a template guide by Smith in U.S. Pat. No. 4,353,672 issued Oct. 12, 1982. The device contains a base plate, carriage assembly, and a template assembly. Although useful for routing certain designs, it is large and cumbersome for cutting large discs such as a tabletop. Other variations in the Smith device providing such guiding assemblies are also large and cumbersome for the simple task of routing circular grooves.
A template device containing various sized circular cutouts from thin material is disclosed in Better Homes and Gardens WOOD February 1990 issue 33, pages 34-35. The perimeter of the cutout is followed with the router equipped with a special piloted bit or template guide. The device, as taught, is useful for routing small circles. The device requiring a separate template for each diameter, also is unweildy for the large diameters like tabletops. Extreme care must be exercised to prevent straying of the cutting bit away from the edge of the template marring the workpiece.
There is a need for the present invention that overcomes the disadvantages heretofore described; that can be safely and accurately operated by the novice as well as the accomplished craftsman being readily adaptable for use with any hand held electric router.